Of course it is! It is even necessary. That is how they will know you
needed a Savior!

** Paul says he "used to persecute the church of God". Do you
suppose that was a half-hearted effort?

No, it was intense. From before his conversion, listen to how Luke
described it in Acts 8:1-3.

** What was the ultimate goal of Paul's abuse?

He wanted to "destroy" the church of Christ!

V.14 ** How do you think that abusive attitude affected his position
among his fellow Jews?

His abuse of Christians made him advance in Judaism "beyond many
of [his] contemporaries".

** What motive was driving Paul and gave him the advantage over his countrymen?

He was "...more extremely zealous...", he was in fact an
ultra fanatic. cf. Acts 22:1-5, 26:9-11

** What did Paul direct his zeal towards?

Ancestral traditions. These were the traditional interpretations and
additions added to the Mosaic Law, they were Rabbinical teachings embodied
in the Mishna.

V.15 ** Paul's life before Christ was vile, consisting of murdering
Christians while trying to earn his way to heaven by keeping the Law.
He was hateful, violent and self-righteous, all at the same time. How
does he now introduce the contrast between his former life and his new
one in Christ?

By using the word "but". He is indicating a strong contrast,
not unlike that in 2Corinthians 5:17.

** We know that Paul's salvation was determined from before the foundation
of the world (Ephesians 1:4). But viewing it from Paul's earthly experience,
at what point did God set the boundaries of Paul's life?

He was "set apart" [aphorizo] from before the time of his
birth! cf. Romans 1:1 (for the gospel)